(1) Field of the Invention
This invention relates to a method of forming a vacuum chamber of a control valve for a variable capacity compressor, and more particularly to a method of forming a vacuum chamber of an internal variable control valve arranged in a variable capacity compressor for compressing low-temperature/low-pressure refrigerant gas within a refrigeration cycle of an air conditioning system for an automotive vehicle, the variable control valve controlling the quantity of the refrigerant gas to be compressed.
(2) Description of the Related Art
In an air conditioning system installed on an automotive vehicle, control of refrigerating capacity in response to a load is performed by varying the capacity of a compressor, since the rotational speed of the engine as a drive source is not constant. Methods of varying the capacity of a compressor include an internal variable control method in which the capacity of a compressor is controlled exclusively within the compressor and an external variable control method in which the capacity of a compressor is electrically controlled based on the results of arithmetic operation performed in response to output signals from various sensors. Description will now be made of a control valve for a variable capacity compressor, which performs the internal variable control.
FIG. 7 is a cross-sectional view showing an example of the construction of a control valve of the internal variable control type, for a variable capacity compressor, which is manufactured by a conventional manufacturing method.
The control valve for a variable capacity compressor is comprised of a valve 1 and a power element 2 for driving the valve. The valve 1 has a port 4 formed in an end portion of a body 3, for communication with a discharge chamber in the variable capacity compressor so as to introduce discharge pressure Pd, a port 5 formed for communication with a crankcase in the variable capacity compressor so as to deliver control pressure, i.e. crankcase pressure Pc, and a port 6 formed for communication with a suction chamber of the variable capacity compressor so as to receive suction pressure Ps. Further, the valve 1 has a ball valve 7 arranged therein such that the ball valve 7 can be seated on a valve seat formed in a refrigerant passage communicating between the port 4 for introducing the discharge pressure Pd and the port 5 for delivering the crankcase pressure Pc, by being urged away from the port 4. The ball valve 7 is urged in the valve closing direction by a spring 8. Spring load by the spring 8 is adjusted by an adjustment screw 9 screwed in the port 4. Further, a shaft 10 axially movably extends along the axis of the body 3, for driving the ball valve 7 through the port 5 on a downstream side of the ball valve 7.
The power element 2 is comprised of a lower housing 11 combined with the body 3 of the valve 1, an upper housing 12, a diaphragm 13 arranged as a pressure-sensitive member in a manner dividing a space enclosed by the lower housing 11 and the upper housing 12, a pair of disks 14, 15 in a manner sandwiching the same, and a spring 16 urging the disk 15 toward the valve 1. The valve-side disk 14 is held in contact with an end face of the shaft 10 extending through a communication hole 17 that communicates between the port 6 for receiving the suction pressure Ps and a valve-side diaphragm chamber.
The upper housing 12 is provided with a capillary tube 18 for evacuating a space or chamber enclosed by the upper housing 12 and the diaphragm 13. The capillary tube 18 is welded in advance to the top portion of the upper housing 12 such that it communicates with a hole formed therethrough. After evacuation of the chamber through the capillary tube 18 is completed, the capillary tube 18 is crushed and cut off, followed by brazing the end of the remaining portion thereof. The end of the capillary tube 18 is thus sealed, whereby the chamber enclosed by the upper housing 12 and the diaphragm 13 becomes a vacuum chamber to prevent changes in temperature and atmospheric pressure from affecting the operation of the diaphragm 13.
However, the conventional control valve for a variable capacity compressor suffers from a problem that the vacuum chamber within the power element is formed through the lots of steps of processing and assembling the power element, welding the capillary tube to the communication hole formed through the upper housing, connecting an evacuator device to the capillary tube to thereby carry out evacuation, crushing and provisionally sealing the capillary tube, cutting off an evacuator device-side portion of the provisionally-sealed capillary tube, and finally brazing the cut portion.
The present invention has been made in view of the above problem and an object thereof is to provide a method of forming a vacuum chamber of a control valve for a variable capacity compressor, the method being capable of forming the vacuum chamber in a power element of the control valve through a reduced number of steps.
To accomplish the above object, according to the present invention, there is provided a method of forming a vacuum chamber of a control valve for a variable capacity compressor, said control valve having a pressure-sensitive member separating said vacuum chamber from another chamber, said pressure-sensitive member controlling an opening degree of said control valve in response to suction pressure of said variable capacity compressor introduced into said another chamber. This method comprises the following steps: joining a periphery of a first housing formed with a small hole and defining said vacuum chamber and a periphery of a second housing to be combined with a valve to each other by caulking, and then brazing a junction of said peripheries; and sealing said small hole in a vacuum atmosphere.
The above and other objects, features and advantages of the present invention will become apparent from the following description when taken in conjunction with the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.